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Reportedly, a casein shake increases muscle mass and strength in response to resistance exercise if drank just before overnight sleep. However, currently there are no studies that have directly addressed if this effect is a result of total protein intake or if a bedtime beverage is better. A review from Frontiers in Nutrition claims that current findings suggest that overnight sleep is a nutritional window for increasing muscle gains. According to Dr. Tim Snijders, an Assistant Professor at Maastricht University, one-night studies have demonstrated that having protein before sleep increases muscle protein synthesis during sleep, and this has brought the idea that over a longer period, having protein supplement before bed “can maximize the strength and muscle mass gains during regular resistance exercise training.” Snijders did a study on this in which he put 44 healthy young men on a 12-week lifting program. Half of them were given a protein shake before sleep each night with 30g of casein and 15g of carbs, whereas the other half just got an energy-free drink. Both groups ended with a bigger squat and larger quads, but the group that was given protein before bed gained more muscle strength and size.

However, there is still a question of whether muscle gains are boosted by protein before sleep or just higher intake overall of protein and calories. One study tried to test this question but did not get statistically significant results because of the low number of participants (26). There are still indirect indicators that protein before sleep is beneficial for healthy young lifters because it can be used to improve protein intake distribution over the day. Muscles only grow and repair when amino acids from protein are available in the blood. A survey conducted among 500 athletes found that they typically consumed more than 1.2g of protein per kilo of their bodyweight across three main meals, but only 7g of protein in the evening, so lower levels of amino acids would be available for muscle growth during sleep. Studies have found that adding protein at bedtime does not affect appetite the next morning. Furthermore, there is concern that intaking calories right before a long period of inactivity may cause fat gain, but according to Snijders, in the study he conducted with casein, the additional consumption of protein did not result in any fat gain. In fact, another study done with a group of 11 young men found that a casein shake before sleep increased the rate of fat burning the next day, most likely because ingesting casein lowers the insulin response to later meals, pushing the body to use more fat. So, overall, although there is not conclusive evidence for adding a protein supplement before bed, it may be worth a try and certainly worth more research.